The present application relates to an optical element, an imaging device, and a driving method. More specifically, the present application relates to an optical element utilizing an electrowetting phenomenon, an imaging device including the optical element, and a method of driving the optical element.
Recently, various optical devices (such as lenses) utilizing an electrowetting phenomenon (electrocapillarity) have been proposed. Such optical devices use a property that the shape of an interface between two liquids enclosed in the optical devices and immiscible with each other is changed through the electrowetting phenomenon. As one of such optical devices, an optical element (aperture mechanism), a so-called liquid iris, configured to control the amount of light to be transmitted using the electrowetting phenomenon has been proposed (refer to, for example, Japanese Unexamined Patent Application Publication Nos. 2006-250967 and 2006-250977).
According to the liquid irises disclosed in Japanese Unexamined Patent Application Publication Nos. 2006-250967 and 2006-250977, an electrically conductive first liquid, and a second liquid that has the same specific gravity as that of the first liquid, that is immiscible with the first liquid, and that has a transmittance higher than that of the first liquid are enclosed inside the liquid irises. Furthermore, a thin film (hydrophilic film) having high affinity with the first liquid and a thin film (water-repellent film) having high affinity with the second liquid are provided on the inner wall of an accommodating chamber that accommodates the first and second liquids. Accordingly, in a static state (in a state in which a liquid iris is not driven), the first liquid is disposed on the hydrophilic film side and the second liquid is disposed on the water-repellent film side in the accommodating chamber.
In each of the liquid irises disclosed in Japanese Unexamined Patent Application Publication Nos. 2006-250967 and 2006-250977, a voltage is applied between an electrode provided on a sidewall of the liquid iris and a transparent electrode provided on an end wall on the light-emitting side to change the shape of the interface between the first liquid and the second liquid through the electrowetting phenomenon. Consequently, a part of the second liquid is pressed onto an end wall of the light-incident side to form an opening through which light is transmitted to the light-incident side of the liquid iris. The size of this opening can be controlled by changing the magnitude of the voltage applied.